Agreed. The new plugs are too hot, and they're burning off all the deposits so you don't see anything on the porcelain. By the time you jet for color, you're almost pig rich and down on power.
Jetting is judged by the fuel ring left at the base of the porcelain where it meets the body. You've got to cut the threads off to see that. I see on one plug where it is too rich because you jetted it up or it idled before you pulled the plugs.
The heat is too far up the ground strap. The plug is marginally too hot. Those fine wire plugs are great.... for an LS that goes 100K between plug changes. And even some LS guys are using copper plugs in high HP motors, because that fine center electrode will glow like rudolph's freaking nose. I built a hot 5.3 LS for my Silvy, and I run the NGK TR55s, which is a copper plug. I just change them more often.
Put a new set of the -8s back in it and check jetting. I'd rather run a plug slightly cold than slightly too hot.
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I could explain all this to the girl at the parts store, but she'd probably call the asylum.
White '67 LeMans 407/TH350/Ford 3.89... RIP
Red '67 LeMans. 407/TH400/Ford 3.25
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